JP3227805B2 - High corrosion resistance stainless steel for high purity gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-corrosion-resistant stainless steel for high-purity gas used in a semiconductor manufacturing process or the like.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing, in recent years, high integration has been advanced, and in the manufacture of devices called ultra LSI,
Processing of a fine pattern of 1 μm or less is required.
In such an VLSI manufacturing process, since minute dust and a trace amount of impurity gas adhere to and are adsorbed on the wiring pattern and cause a circuit failure, both the reaction gas and the carrier gas used must have high purity. It is necessary to reduce the amount of fine particles and impurity gas. Therefore, in the high-purity gas pipes and members, it is required that the amount of fine particles (particles) and gas as contaminants released from the surface be as small as possible.

[0003] Further, as a semiconductor manufacturing gas, nitrogen,
Since corrosive gases such as chlorine and chlorosilanes are used in addition to inert gases such as argon, members that come into contact with these corrosive gases naturally need to have high corrosion resistance.

Conventionally, such gas pipes and members for semiconductor production have been smoothed until the surface roughness (Rmax) becomes 1 μm or less in order to reduce the adhesion and adsorption of dust and moisture. As a method of such surface smoothing,
Examples include cold drawing, mechanical polishing, and electrolytic polishing.
The highly smooth material having x of 1 μm or less is mainly manufactured by electrolytic polishing. Thereafter, the pipe or the like having a smooth surface is washed with high-purity water and dried with high-purity gas to obtain a product.

As a material for gas pipes and members for semiconductor production, austenitic stainless steel, especially SU
S 316L is mainly used.

Japanese Patent Application Laid-Open No. 63-161145 discloses a steel pipe for a clean room in which non-metallic inclusions are reduced by regulating the contents of Mn, Si, Al, O (oxygen) and the like. A high-purity austenitic stainless steel other than the standard steel is disclosed, which is intended to reduce the generation of particles from the inner surface of the pipe.

[0007]

SUMMARY OF THE INVENTION In order to reduce the generation of particles which are indispensable for the performance of stainless steel pipes for high-purity gas pipes, it is necessary to smooth the inner surfaces of the pipes and to reduce the generation of particles.
The effect can be expected by reducing nonmetallic inclusions as disclosed in JP-A-63-161145. However, the existing stainless steel does not have sufficient performance in the corrosion resistance of the base metal and the weld required for high-purity gas piping, particularly for corrosive gas piping.

[0008] An object of the present invention is to provide a high-purity gas stainless steel having excellent corrosion resistance to corrosive gases in stainless steel whose surface has been smoothed by electrolytic polishing.

[0009]

Means for Solving the Problems In order to solve this problem, the present inventors examined the relationship between the corrosion resistance of the electrolytically polished surface and the composition of the surface coating on stainless steels having various chemical compositions and their welds. did. As a result, S and O, which form non-metallic inclusions and generate particles and cause corrosion, naturally reduce the contents of Si and Mn.
On the other hand, by adding an appropriate amount of Al, the corrosion resistance is improved by the surface film formed during the electrolytic polishing treatment,
It has been found that reducing the Mn content improves the corrosion resistance, particularly in the heat affected zone. This is because, in the oxide film mainly composed of Cr generated by electrolytic polishing, the base material Si, Mn
This is because, when the content is reduced, the impurities Si and Mn in the film are reduced, and the Cr content is increased. Even in the weld heat affected zone of the electrolytically polished steel pipe, by reducing the Mn content, a surface film having a high Cr content due to electrolytic polishing is maintained, and deterioration of corrosion resistance does not occur. At this time, the insufficient amount of deoxidation due to the reduction of Si and Mn,
It was also found that Al can be supplemented by containing Al, and that the Al content does not adversely affect the corrosion resistance within the range.

The gist of the present invention resides in the following high corrosion resistant stainless steel for high purity gas.

(1) Ni: 10 to 40%, Cr: 15 to 30% by weight
% And Al: more than 0.01 % and 0.5% or less, with the balance being F
e and unavoidable impurities, the content of C is 0.03% or less, the content of Si is 0.1% or less, the content of Mn is 0.2% or less, the content of P is 0.01% or less, the content of S is 0.003% or less, and the content of O is 0.01% or less. The high corrosion resistant stainless steel for high purity gas, characterized in that the Ni-bal. Ni-bal. = Nieq.-1.1% Creq. +8.2 However, Nieq. =% Ni +% Cu + 0.5% Mn + 30 (% C +%
N) Creq. =% Cr + 1.5% Si +% Mo +% W

(2) By weight%, Ni: 10 to 40%, Cr: 15 to 30
% And Al: more than 0.01 %, 0.5% or less, and Cu: 3%
In the following, one or more of Mo: 9% or less, W: 6% or less, and N: 0.4% or less are contained, and the balance consists of Fe and unavoidable impurities. The impurity C is 0.03% or less and Si is 0.1% or less. % Or less, Mn is 0.2% or less, P is 0.01% or less, S is 0.003% or less, and O is 0.01% or less.
A high corrosion resistant stainless steel for high purity gas, wherein the bal. value is 0 or more and less than 3.

Ni-bal. = Nieq.-1.1% Creq. + 8.2 where Nieq. =% Ni +% Cu + 0.5% Mn + 30 (% C +%
N) Creq. =% Cr + 1.5% Si +% Mo +% W

[0014]

The reasons for determining the chemical composition of the stainless steel of the present invention as described above will be described.

Ni, Cr: Ni and Cr are important elements for the corrosion resistance and structure control of steel. In the present invention, Ni is set to 10 to 40% and Cr is set to 15 to 30% in order to maintain the structure of the austenitic stainless steel and to maintain higher corrosion resistance. Outside these ranges, desirable corrosion resistance and metallographic structure cannot be obtained.

Al: If Al is present in excess, the formation of oxide-based nonmetallic inclusions is promoted, the cleanliness of the steel is reduced, and as described above, the steel is not suitable for use in the present invention. However, in the present invention, since the contents of other Si and Mn having a deoxidizing action are regulated to be low, in order to perform a desired deoxidation and reduce O (oxygen) in the steel, an appropriate amount of Al is used. It is inevitable to add. If the Al content is less than 0.01%, deoxidation tends to be insufficient, and if it exceeds 0.5%, oxide-based nonmetallic inclusions are easily formed.

C: C is desirably low in order to precipitate Cr carbide and reduce corrosion resistance. In consideration of the use of the steel of the present invention for a strongly corrosive gas, the content is set to 0.03% or less.

Si, Mn: One of the features of the present invention is to reduce the contents of Si and Mn. If the contents of both Si and Mn are excessive, they are concentrated as impurities in the electropolishing film, reduce the Cr content in the film, and deteriorate the original corrosion resistance of the Cr oxide film. In addition, Mn concentrates particularly on the surface film of the heat affected zone, and at the same time reduces the Cr content in the film,
Deterioration of corrosion resistance. The limit to which this degradation can be tolerated is Si
0.1% and 0.2% for Mn. If these concentrations are exceeded, excellent corrosion resistance cannot be obtained. Therefore, the content of Si is 0.1%
Hereinafter, the content of Mn is set to 0.2% or less.

P, S: If the content of P exceeds 0.01% and the content of S exceeds 0.003%, both of them are harmful to corrosion resistance and hot workability. In particular, S is very small
Generates MnS and is extremely harmful to corrosion resistance. Therefore, P
Is 0.01% or less and S is 0.003% or less.

O: O (oxygen) is an element that forms nonmetallic inclusions along with S, and needs to be reduced as much as possible. As long as it does not adversely affect corrosion resistance and steel cleanliness
0.01% or less.

Cu, Mo, W, N: In the present invention, the main purpose is to improve the corrosion resistance by improving the composition of the electrolytic polishing film, but it is of course possible to improve the corrosion resistance of the alloy itself. For this reason, the corrosion resistance improving element may be added within a range that does not deteriorate other properties such as hot workability and weldability. C
Each of u, Mo, W, and N is an element having an effect on improving corrosion resistance, and one or more of Cu: 3% or less, Mo: 9% or less, W: 6% or less, and N: 0.4% or less. Two or more are selected and contained. If these contents are exceeded, the effect of improving corrosion resistance is saturated.

Ni-bal. Value: When the Ni-bal. Value is less than 0, only the unstable austenite structure containing a ferrite phase can be obtained in the stainless steel of the present invention, so that the mechanical properties and corrosion resistance deteriorate. On the other hand, if it is 3 or more, the hot workability decreases, and there is no problem in the production of small ingots and the like in the laboratory.
During rolling, cracks are likely to occur. Therefore, the Ni-bal. Value calculated from the alloy element content of the steel of the present invention is 0 or more and 3 or more.
Less than.

Incidentally, Ca, Mg, B and rare earth elements may be added to the steel of the present invention in order to improve hot workability.

[0024]

EXAMPLES Outer diameters having six kinds of chemical compositions shown in Table 1
The inner surface of a 6.4 mm, 1 mm thick, 4 m long SUS316L stainless steel seamless pipe is electropolished to an Rmax of 0.7μ.
After the surface was smoothed so as to obtain m, it was washed with high-purity water and dried at 120 ° C. by passing 99.999% Ar gas. 1 m of these steel pipes were butt-welded for the same steel type under the conditions shown in Table 2 to produce samples.

The Cr content of the inner surface coating of the tube was measured by a secondary ion mass spectrometer at 4 mm from the melting boundary of the base metal and the welded portion.
It was measured by a method of performing elemental analysis in the depth direction on the inner surface of the cross section of the distant heat-affected zone, and the highest value of the Cr content (atomic%) in the metal element was compared.

In the corrosion test, a 40 mm long sample centered on the welded portion was cut out of the remaining welded steel pipe, and these were impregnated with an aqueous ferric chloride solution and a filter paper having a width of 5 mm and a length of 20 mm was used. Was adhered to a portion centered on the welded portion on the inner surface of the pipe, and left standing at 25 ° C. for 6 hours, and the occurrence of pitting corrosion was visually observed. At this time, as shown in Table 3, the corrosion resistance was evaluated by changing the concentration of ferric chloride in the corrosive liquid in various ways and by limiting the concentration at which pitting occurred. Table 3 summarizes the results of these tests.

As can be seen from Table 3, in the stainless steel having a chemical composition within the range of the present invention, in the electropolished film,
The Cr content is high, and thus the ferric chloride concentration at which pitting corrosion occurs in both the base metal and the welded portion is high, indicating good corrosion resistance.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

According to the present invention, it is possible to obtain a high-purity gas stainless steel having excellent corrosion resistance in both the base material and the welded portion.

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00 302 C22C 30/00 C22C 38/40 C22C 38/44

Claims (2)

(57) [Claims] (1) In terms of% by weight, Ni: 10 to 40%, Cr: 15 to 30%, and Al: more than 0.01 % to 0.5% or less, with the balance being Fe and unavoidable impurities, 0.03% or less,
Si is 0.1% or less, Mn is 0.2% or less, P is 0.01% or less, S
Is 0.003% or less and O is 0.01% or less, and the Ni-bal. Value given by the following formula is 0 or more and less than 3. Ni-bal. = Nieq.-1.1% Creq. +8.2 However, Nieq. =% Ni +% Cu + 0.5% Mn + 30 (% C +%
N) Creq. =% Cr + 1.5% Si +% Mo +% W 2. In terms of% by weight, Ni: 10 to 40%, Cr: 15 to 30% and Al: more than 0.01 %, 0.5% or less, Cu: 3% or less, Mo: 9% or less, W: 6% And N: contains at least one of 0.4% or less, and the balance consists of Fe and unavoidable impurities. The impurities C are 0.03% or less, Si is 0.1% or less, Mn is 0.2% or less, and P is 0.01% or less. %, S is 0.003% or less, O is 0.01% or less, and Ni-
A high corrosion resistant stainless steel for high purity gas, wherein the bal. value is 0 or more and less than 3. Ni-bal. = Nieq.-1.1% Creq. +8.2 However, Nieq. =% Ni +% Cu + 0.5% Mn + 30 (% C +%
N) Creq. =% Cr + 1.5% Si +% Mo +% W